Base metal for vitreous enamel



Patented Apr. 2,1935

UNITED STATES PATENKT OFFICE BASE METAL roa-vrrnsous ENAMEL Clarence H. Butts, Monroe, Mich., assignor to The Newton Steel Company, Monroe, Mich, a

. corporation of Ohio "No D'ra'wing. Application July 11, 1932, 1 Serial No. 622,019

2 Claims.

This invention relates, as indicated, to base metal for vitreous enamel and more particularly, to sheet steel adapted toreceive a coating of vitreous enamel and when so coated, be employed 6 as a unit of construction in which enameled sheet metal to give off occluded gases during the firing operation and second, the tendency of the sheet metal blanks to warp or sag and otherwise lose their shape during the firing operation.

As is well known to those familiar with the art, vitreous enamel finishes are usually produced by applying what is'commonly termed a ground coat to a suitable metallic, base, firing such ground coat and then applying either one or more finish coats and then firing such fi'ni'sh; coats.

For a number ofreasons which need not be gone into at this time, the above referred to ground coat is usually dark in color, in the most instances, a very dark blue which is nearly' black. The finished coats, however; are usually light in color, the majority bein pure white.

The occurrence of minute dark colored specks has been observed in the production of a large percentage of light colored vitreous enamel finishes. It has been found that these dark specks are due to'gases which are given up by the base metal during the firing of the finish coat, such gas bubbling through the ground coat and causing a small quantity of such ground coat to be driven through the finish coat to produce these dark specks;

As above indicated, another-principal difficulty encountered in the manufacture of vitreous enamel finished sheet metal articles, especiallywhen such articles are formed into unusual shapes, is the ,tendency of the metal blank to warp or g out of shape during the firing of the vitreous e mel finish. If the warping is considerable, the blank must be scrapped for the reason that a distortion of the blank afterthe enamel has been fired will cause the occurrence ofhair cracks and like imperfectionswhen fabricated. Y 3

50 It is among the objects of my invention'to pro fvide a base metal for vitreous enamel finishes which shall have none of the above named undesirable characteristics. Other objects of my invention will appear as the description proceeds.

, For purposes of convenience, a giving in the past, i. e., first, the tendency of the sheet the range of percentages of the different important ingredients in the steel previously employed as a base metal for enamel finishes is reproduced below:

Sulphur Phosphorus .004 to .020 Carbon -i... .012 to .030 Manganese I .030t0 .080

' Si1icon Trace Iron (by difference) 99.929 to 99.830

The process comprising my inventionifor pro- -ducing a non-bubbling and non-warping base metal comprises refining the metal in the furnace to apoint where the carbon content is under 025% and the manganese content is under 060%, After the metal has been so refined, the proper amount of deoxidizing agents, 1. e. manganese and silicon, are added so that the essential ingredients in the/resultant metal analyze as follows: V

su1phur .0251 I .040 Phosphorus .004 to .020 Carbon .012 to, .060 Manganese '.040 to .300 I Silicon .030 to .100 Iron (by difference) 99.889 to 99.480

- In the above table the range of silicon content has been given as between .030 and .100 and steel .30

.half to two pounds, of aluminum or aluminum titanium perton of metal depending upon the state of oxidation of the molten bath.

Metal having'the above treatment and com,- position has been found to be far superior to ordinary killed steel, for the reason that while ordinary killed steel may not appreciably bubblerlduring the firing operation, in the vitreous enamel process, nevetherless, such kil1ed" steel is bject to excessive warpage or sag; whereas,

' steel manufactured according to the processcom-f prising my invention and when properly processed in sheet form; as presently to be described, does not evolve occluded, gas during the firing operation and doesnot warp or sag an appreciable amount. 5

Ordinary silicon killed steels are very soft at elevated temperatures and accordingly, do notretain their shape during the enamellua process After the metal of the above referred to desirable composition and produced in the manner specified has been rolled into sheets, such sheets are box annealed at a temperature of from 1200 Fahrenheit to 1500 Fahrenheit, such box annealing preferably being followed by normalizing or open annealing the sheets, if it is necessary, to produce the proper physical results. Normalization or open annealing will not prevent warpage or sag without first box annealing the sheets. So long as the sheets are box annealed, fairly good results may be secured by normalizing before box annealing. However, best results are obtained if the normalizing step follows the box annealing.

The manner of producing the base metal and its composition, as above set forth, may be sat isfactorily employed in vitreous enameling processes without appreciable bubbling and hence, a light colored coat may be, applied to a dark colored ground coat without the occurrence of objectional spots incidental to a bubbling action.

-The metal treated in the manner described also' is characterized by the fact that it retains its shape and does not warp or sag during the firing operation.

Other modes of applying the principle of my invention may be employed instead of the one explained, change being made as regards the materials employed, provided the ingredients stated by any of the following claims or the equivalent of such stated ingredients be emplayed.

I therefore particularly point outand distinctly claim as my invention:-

1. The process of manufacturing sheet steel suitable for receiving a fired coat of vitreous enamel which includes the steps of refining the steel to a stage where the carbon content is below 0.025% and the manganese content is below 0.060%, then adding to the steel alloying elements in sufficient quantities so that the steel has substantially the following composition:

Sulphur from 0.025% to 0.0 l%

Phosphorus from Carbon from Manganese from 040% to 300% Silicon from '.030% to .100%

Sulphur from 0.025% to 0.040%

Phosphorus from 004% to 020% Carbon from 012% to 060% Manganese from 040% to 300% Silicon from 030% to .100%

the remainder being substantially iron, rolling such metal to sheet form, box annealing such sheets at a temperature from about 1200 F. to about 1500 F. and then normalizing such sheets.

CLARENCE H. BUTTS. 

